I tried the zita stuff some time ago, it seems to work differently than expected.
For once, I could only start it if there was an alsa app running and using the loopback. I don't know if that's intended, but alsa_in/out already works fine, so I skipped this.

no, it works as a generic python(3) script. You just need to have jacklib.py at its side (and the asoundrc file set properly, of course).
The previous version had a small jacklib version built-in, but it's much easier to maintain and fix if it uses the the external jacklib.py.

Is there any update on this? I got cracking with the alsa in/out bridge which is totally gone with the zita bridge. However to get the zita bridge running after a reboot is not that straight forward. I stopped cadence and connections several times and re-opend firefox, etc. ... At some point it worked. CPU usage is < 1% (as seen in system monitor zita-j2a/a2j).

One more question: Do I need to do anything else (theoretically) besides starting jack and the alsa -> loop -> jack with zita? E.g. do I have to modify the .asoundrc - file? Once I did some changes in the file (replacing 44100 with 48000), but somehow it was overwritten again. Shoukd I add the zita bridge in this file somehow?